Rainfall deficits worsen following a dry September

Rainfall deficits have expanded and intensified over the southern half of
the country as a result of widespread below to very much below average
September rainfall. Averaged over the Murray-Darling Basin (MDB), it was
the driest September in the historical record back to 1900. Unless October
and November are wetter than average, 2006-07 will be one of the very few
instances in history where the MDB has suffered a winter-spring drought in
successive years. The other years when this has occurred were 1918-19 (the
latter was extremely dry), and 1940-41, with 1940 being very dry. In each
of the years 1927, 1928, and 1929, large parts of the MDB had a winter-spring
rainfall total in decile 3 or lower, although individually none of the years
was extremely dry.
See September
rainfall pattern

4-month rainfall deficiencies

Since the start of winter, South Australia has been the worst hit state, with
the four-month average being the lowest on record at just 26 mm. At the
yearly time-scale, rainfall deficiencies are evident in all states and
territories, although the NT has only a few small patches. As September 2007
had generally similar rainfall to September 2006 in the areas with
twelve-month deficiencies, there was little change to their pattern compared
with the situation at the end of August.

For the 3-month period from June to September 2007, an area
of serious to severe rainfall deficiencies covered most of SA, southwest
Queensland, western NSW, northern Victoria, regions in the southern NT,
scattered parts of WA and a small patch in northeast Tasmania. Several
regions had record low totals, most notably in SA, Queensland and New South
Wales.

5-month rainfall deficiencies

Rainfall deficiencies for the 5-month period from May to
September 2007 were widespread across the southern half of Western Australia.
SA was also affected, but to a much lesser extent than for the four-month
period.

12-month rainfall deficiencies

For the 12-month period from October 2006 to September
2007, zones or regions of rainfall deficits existed near the southwest and
west coasts of WA (generally south of Shark Bay), along parts of coastal SA,
in northern and eastern Tasmania, in a band from south-central Victoria to
the tablelands and western slopes in southeastern NSW, and in southeast
Queensland and adjacent parts of far northern NSW. Record low falls for this
particular 12-month period were recorded just to the east of Melbourne, and
along WA’s west coast between Shark Bay and Geraldton.

The deficiencies discussed above have occurred against a backdrop of
multi-year rainfall deficits and record high temperatures that have severely
stressed water supplies in the east and southwest of the country. Several
years of above average rainfall are required to remove the very long-term
deficits. Furthermore, the combination of heat and drought during the past
five to ten years over the MDB and southeastern Australia, is outside the
typical range of variability experienced during the previous 100 years.